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WINTER 2005
Figure 4 - The Sidewall Impact Model uses 2, 4 or 6 springs
projecting laterally from the wheel plane.
Figure 5 - The Sidewall Impact Model is ideally suited for
simulating curb impact.
Technical Newsletter
Figure 7 - The Soft Soil Model allows the tire to sink into the
terrain, producing a drag force on the tire.
Soft Soil Model
The Soft Soil Model is based on research performed by
M.G. Bekker at the University of Michigan. The purpose
of part of the original research was to predict the
performance and tractive effort requirements of the
lunar rover. In the Soft Soil Model (see Figure 7), tire
sinkage into the soil is calculated using an empirical
model developed by Bekker. Tire Fx’,Fy’ forces are
calculated based on the sinkage. This model is ideal for
calculating tire drag for a vehicle that has left the
roadway and is traveling though soft dirt. The model is
also useful for predicting soil-tripped rollover. Soil
coefficients may be provided for individual surfaces
using the Environment 3-D Editor.
Implementation
The new Tire-Terrain option has been added to the
Event Editor’s Wheels Set-up dialog (see Figure 8), as
an extension to the existing options (Tire Blow-out,
Wheel Damage and Brake). Like the existing options,
the new tire-terrain options may be applied separately
to individual tires. For example, all tires may use the
default point contact model. Alternatively, the left front
tire may use the radial spring tire model, while the right
rear inside tire (of a dual tire set) may use the soft soil
model and the right rear outside tire might use the
sidewall impact model. This approach allows total
flexibility to model virtually any foreseeable situation.
Figure 6 - Simulation of curb-tipped rollover using the new
Sidewall Impact Tire-Terrain Model.
Several new time domain results are produced when
the new tire-terrain models are invoked. These results
are included in the HVE’s Variable Output, both in Key
Results windows (Event Editor) and in the Variable
Output Table (Playback Editor). These parameters
include tire sidewall forces and moments, and tire
sinkage and sinkage-related forces.
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